diff --git a/Documentation/Examples/em_shower.cc b/Documentation/Examples/em_shower.cc
index 594a95845c9a2e8d8640aeda4c7847ed591d9420..297ab1f67d62426e4086890b9998b8c0592194fb 100644
--- a/Documentation/Examples/em_shower.cc
+++ b/Documentation/Examples/em_shower.cc
@@ -151,8 +151,8 @@ int main(int argc, char** argv) {
   process::longitudinal_profile::LongitudinalProfile longprof{showerAxis};
 
   Plane const obsPlane(showerCore, Vector<dimensionless_d>(rootCS, {0., 0., 1.}));
-  process::observation_plane::ObservationPlane observationLevel(obsPlane,
-                                                                "particles.dat");
+  process::observation_plane::ObservationPlane observationLevel(
+								obsPlane, Vector<dimensionless_d>(rootCS, {1., 0., 0.}), "particles.dat");
 
   auto sequence = process::sequence(proposalCounted, em_continuous, longprof, cut,
                                     observationLevel, trackWriter);